Liquid crystal display device and alignment film material thereof

ABSTRACT

To form an optical alignment film having large anchoring strength and suppress an AC afterimage of a liquid crystal display device, in a liquid crystal display device of an IPS mode. In an alignment film material subjected to optical alignment processing, polyimide which becomes a rigid high molecule and polyimide which becomes a flexible high molecule are mixed and used. The material of the present invention can easily rotate oligomer after irradiating polarized ultraviolet rays and improve a UV-absorbed two-color ratio of an alignment film. Accordingly, an anchoring strength for liquid crystals by the alignment film is large to suppress an AC afterimage.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2011-114470 filed on May 23, 2011, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display device, andmore particularly, to a liquid crystal display device that grants analignment control capability by irradiating light to an alignment film.

BACKGROUND OF THE INVENTION

In a liquid crystal display device, a TFT substrate in which a pixelelectrode and a thin film transistor (TFT) are formed in matrices and anopposed substrate where a color filter is formed at a placecorresponding to the pixel electrode of the TFT substrate is installedto be opposed to the TFT substrate, and liquid crystals are interposedbetween the TFT substrate and the opposed substrate. An image is formedby controlling light transmittance by liquid crystal molecules for eachpixel.

Since the liquid crystal display device has a flat shape and a lightweight, the use of the liquid crystal display device has been widened tovarious fields such as a large-sized display device such as a TV, acellular phone, or a digital still camera (DSC). Meanwhile, a viewingangle characteristic is problematic in a liquid crystal display device.The viewing angle characteristic is a phenomenon in which luminance ischanged or chromaticity is changed when a screen is viewed from thefront side and when the screen is viewed from an inclined direction. Anin plane switching (IPS) mode in which the liquid crystal molecules areoperated by horizontal electric fields has an excellent viewing anglecharacteristic.

As a method of performing alignment processing of an alignment film usedin the liquid crystal display device, that is, granting an alignmentcontrol capability, a method of processing by rubbing as the related artis used. In the alignment processing by the rubbing, the alignmentprocessing is performed by rubbing the alignment film with a cloth, butmeanwhile, there is an optical alignment method of granting thealignment control capability by non-contact with the alignment film.Since the IPS mode does not need a pretilt angle, the optical alignmentmethod can be applied. Japanese Patent Application Laid-Open Nos.2004-86047, 2004-20658, 2004-163646, 2004-341030, 2004-346311,2005-215029, and 2006-17880 are known examples associated with theoptical alignment film and they disclose that a cross-linking reaction,a cleavage reaction, or a dimerization reaction of the molecules iscaused within a thin film by irradiating linearly polarized ultravioletrays and anisotropy is granted to an arrangement of the molecules withinthe thin film.

SUMMARY OF THE INVENTION

In optical alignment processing in the related art, image burn called anAC afterimage occurs more easily as compared with rubbing. The ACafterimage is an afterimage generated because an initial alignmentdirection is deviated from a direction at the time of firstmanufacturing of the liquid crystal display device when the liquidcrystal display device operates over a long time. The AC afterimage isirreversible and irrecoverable.

The AC afterimage can be improved by (1) improvement of alignmentorderliness of an alignment film, (2) improvement of mechanical strengthusing modulus of elasticity and hardness of the alignment film asparameters, and (3) improvement of affinity between the alignment filmand liquid crystals. Among them, improvement of alignment orderliness ofthe alignment film is particularly effective in reducing the ACafterimage.

However, in the optical alignment method, the effective method forimproving the alignment orderliness has not been discovered. The presentinvention has been made in an effort to improve the alignmentorderliness of the alignment film and suppress generation of the ACafterimage in optical alignment processing.

The present invention has been made in an effort to provide a liquidcrystal display device and detailed means is as follows. That is, anembodiment of the present invention provides a liquid crystal displaydevice, including: a TFT substrate where an alignment film is formed ona pixel having a pixel electrode and a TFT; an opposed substrate opposedto the TFT substrate and where an alignment film is formed on a colorfilter; and liquid crystals interposed between the alignment film of theTFT substrate and the alignment film of the opposed substrate, whereinthe alignment films are subjected to optical alignment processing, andthe alignment films use an alignment material (having a flexiblestructure) acquired by esterifying the dehydrated condensate of materialrepresented by (Chem. 1) (1,2-bis(4-aminophenyl)ethane when R1 and R2are hydrogen and n=2) and material represented by (Chem. 3)(1,3-dimethyl cyclobutane tetracarboxylic acid dianhydride when R3 andR4 are methyl) and an alignment material (having a rigid structure)acquired by esterifying the dehydrated condensate of materialrepresented by (Chem. 2) (paraphenyldiamine) and material represented by(Chem. 3) (1,3-dimethyl cyclobutane tetracarboxylic acid dianhydridewhen R3 and R4 are methyl).

wt % with respect to the entire flexible structure is more than 0 wt %and 80 wt % or less and more preferably, 60 wt % or more or 80 wt % orless.

According to embodiments of the present invention, since an orderparameter (OP) can be increased and an anchoring strength can beincreased in an optical alignment film, a liquid crystal display devicehaving the optical alignment film suppressing an AC afterimage can beimplemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a liquid crystal display device ofan IPS mode;

FIG. 2 is a plan view of a pixel electrode of FIG. 1.

FIG. 3 is a process diagram illustrating a liquid process of analignment film;

FIG. 4 is a mimetic diagram illustrating a film structure for eachprocess in optical alignment processing in the related art and accordingto an embodiment of the present invention; and

FIG. 5 is a graph illustrating a relationship between wt % of a flexiblestructure and an order parameter (OP) of an alignment film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Prior to describing an embodiment of the present invention, a structureof a liquid crystal display device of an IPS mode to which the presentinvention is applied will be described. FIG. 1 is a cross-sectional viewillustrating a structure in a display area of a liquid crystal displaydevice of an IPS mode. Various electrode structures of the liquidcrystal display device of an IPS mode are proposed and commercialized.The structure of FIG. 1 is a structure which is widely used at present,and in brief, a comb-shaped pixel electrode 110 is formed by insertingan insulating film on an opposed electrode 108 formed as a plane. Inaddition, an image is formed by controlling light transmission of aliquid crystal layer 300 for each pixel by rotating a liquid crystalmolecule 301 with a voltage between the pixel electrode 110 and theopposed electrode 108. Hereinafter, the structure of FIG. 1 will bedescribed in detail. Further, a configuration of FIG. 1 is described asan example, but the present invention may also be applied to a liquidcrystal display device of an IPS type other than FIG. 1.

In FIG. 1, a gate electrode 101 is formed on a TFT substrate 100 made ofglass. The gate electrode 101 is formed on the same layer as a scanningline. In the gate electrode 101, a MoCr alloy is laminated on an AlNdalloy.

A gate insulating layer 102 made of SiN covers the gate electrode 101. Asemiconductor layer 103 is formed by an a-Si layer at a position on thegate insulating layer 102 opposed to the gate electrode 101. The a-Silayer is formed by plasma CVD. The a-Si layer forms a channel part of aTFT, and a source electrode 104 and a drain electrode 105 are formed onthe a-Si layer with the channel part interposed therebetween. Further,an n+Si layer (not shown) is formed between the a-Si layer and thesource electrode 104 or the drain electrode 105. The reason is that thesemiconductor layer and the source electrode 104 or the drain electrode105 ohmic-contact each other.

The source electrode serves as an image signal line and the drainelectrode 105 is connected with the pixel electrode 110. Both the sourceelectrode 104 and the drain electrode 105 are formed on the same layersimultaneously. In the embodiment, the source electrode 104 or the drainelectrode 105 is made of the MoCr alloy. When electrical resistance ofthe source electrode 104 or the drain electrode 105 is to be reduced,for example, an electrode structure in which the AlNd alloy issandwiched with the MoCr alloy is used.

An inorganic passivation layer 106 made of SiN covers the TFT. Theinorganic passivation layer 106 protects, in particular, the channelpart of the TFT from impurities 401. An organic passivation layer 107 isformed on the inorganic passivation layer 106. The organic passivationlayer 107 serves to protect the TFT and planarize the surface and thusis formed to be thick. The thickness thereof is in the range of 1 μm to4 μm.

In the organic passivation layer 107, a photosensitive acrylic resin, asilicon resin, or a polyimide resin is used. A through-hole 111 needs tobe formed at a portion on the organic passivation layer 107 where thepixel electrode 110 and the drain electrode 105 are connected with eachother; since the organic passivation layer 107 is photosensitive, thethrough-hole 111 may be formed by exposing and developing the organicpassivation layer 107 itself without using photoresist.

The opposed electrode 108 is formed on the organic passivation layer107. The opposed electrode 108 is formed by sputtering indium tin oxide(ITO) which is a transparent conductive layer to an entire display area.That is, the opposed electrode 108 has a planar shape. After the opposedelectrode 108 is formed on the entire area by sputtering, only thethrough-hole 111 for conducting the pixel electrode 110 and the drainelectrode 105 is removed by etching the opposed electrode 108.

An upper insulating layer 109 made of SiN covers the opposed electrode108. After the upper insulating layer 109 is formed, the through-hole111 is formed by etching. The through-hole 111 is formed by etching theinorganic passivation layer 106 by the upper insulating layer 109 asresist. Thereafter, the ITO forming the pixel electrode 110 is formed bysputtering by covering the upper insulating layer 109 and thethrough-hole 111. The pixel electrode 110 is formed by patterning thesputtered ITO. The ITO forming the pixel electrode 110 is deposited evenon the through-hole 111. In the through-hole 111, the drain electrode105 and the pixel electrode 110 that extend from the TFT are conductedto each other and an image signal is supplied to the pixel electrode110.

One example of the pixel electrode 100 is illustrated in FIG. 2. Thepixel electrode 110 is a comb-shaped electrode. A slit 112 is formedbetween combs. The planar opposed electrode 108 is formed below(downward) the pixel electrode 110. When the image signal is applied tothe pixel electrode 110, a liquid crystal molecule 301 is rotated by anelectric force line generated between the opposed electrodes 108 throughthe slit 112. As a result, the image is formed by controlling lightpassing through a liquid crystal layer 300.

FIG. 1 describes this aspect as the cross-sectional view. The slit 112shown in FIG. 1 is formed between the comb-shaped electrode and thecomb-shaped electrode. A predetermined voltage is applied to the opposedelectrode 108 and a voltage by the image signal is applied to the pixelelectrode 110. When the voltage is applied to the pixel electrode 110,the electrical force line is generated to rotate the liquid crystalmolecule 301 in the direction of the electrical force line, therebycontrolling transmission of light from a backlight, as shown in FIG. 1.Since the transmission from the backlight is controlled for each pixel,the image is formed.

In the example of FIG. 1, the opposed electrode 108 having the planarshape is disposed on the organic passivation layer 107 and thecomb-shaped electrode 110 is disposed on the upper insulating layer 109.Contrary to this, however, the pixel electrode 110 having the planarshape may be disposed on the organic passivation layer 107 and thecomb-shaped opposed electrode 108 may be disposed on the upperinsulating layer 109. An alignment film 113 for aligning the liquidcrystal molecules 301 is formed on the pixel electrode 110. Thealignment film 113 is subjected to the optical alignment processing.

In FIG. 1, an opposed substrate 200 is installed with the liquid crystallayer 300 interposed between the substrates. A color filter 201 isformed inside the opposed substrate 200. Red, green, and blue colorfilters 201 are formed for each pixel, and a color image is formed.Black matrices 202 are formed between the color filters 201 to improve acontrast of the image. Further, the black matrices 202 also serve as alight shielding layer of the TFT and prevent optical current fromflowing on the TFT.

An overcoat layer 203 is formed by covering the color filter 201 and theblack matrices 202. Since the surfaces of the color filter 201 and theblack matrices 202 are uneven, the surfaces are planarized by theovercoat layer 203. The alignment film 113 for determining initialalignment of the liquid crystals is formed on the overcoat layer 203.The alignment film 113 is subjected to the optical alignment processingas well.

In the present invention, an AC afterimage is reduced by improvingalignment orderliness of the optical alignment film in FIG. 1. Theinventors theoretically have analyzed the relationship among physicalvalues such as a molecular extinction coefficient and a photolyticquantum yield in an alignment film material and process parameters(heating temperature, heating time, and an exposure time) and thealignment orderliness. They have revealed that a molecular extinctioncoefficient ratio between an axial direction and a short-axis directionof molecules of the alignment film material and a change in moleculardirection of oligomer generated by photolysis of polyimide bypolarization exposure play an important role in improving the alignmentorderliness. Herein, the molecular extinction coefficient ratio isεp/εv, εp is a molecular extinction ratio of a long-axis direction ofthe molecules of polyimide, and εv is a molecular extinction ratio of ashort-axis direction of the molecules of polyimide.

As the molecular extinction coefficient ratio between the long-axisdirection of the molecules and the short-axis direction of the moleculesincreases, a difference in density of polyimide between a paralleldirection and an orthogonal direction to an electric field vector bypolarization exposure increases, and as a result, the alignment filmhaving the high alignment orderliness may be formed. In general,polyimide having a large molecular extinction coefficient ratio betweenthe long-axis direction of the molecules and the short-axis direction ofthe molecules is a high molecule in which the molecules have highlinearity and are rigid.

Meanwhile, the amount of directional change of oligomer is increased ashigh as polyimide (polyimide with an alkyl chain as a main chain and inwhich molecule-axis rotation is induced by heating after polarizationexposure) having high flexibility. As a result, in order to balance theimprovement of the alignment orderliness in the photolysis and theimprovement of the alignment orderliness in the polarization exposure,opposite polyimide characteristics require to be offset.

The inventor has discovered that a conflicting relationship betweenrigidity and flexibility required for the optical alignment film can beoffset by mixing (rigid) polyimide having the high molecular extinctioncoefficient ratio with polyimide having high flexibility and analignment film having high-alignment orderliness can be implemented.Hereinafter, the content of the present invention will be described indetail with reference to examples.

Example 1

FIG. 3 is a diagram illustrating a process of forming an alignment filmsubjected to optical alignment processing. The process of FIG. 3 iscommon to the TFT substrate, and the opposed substrate. The alignmentfilm is applied to the TFT substrate with the pixel electrode or theopposite substrate with the overcoat layer in FIG. 1. The alignment filmmay be applied by using a spin coating method, an inkjet method, a spraycoating method, or a rod coating method.

The alignment film material contains an alignment material acquired byesterifying dehydrated condensate of material represented by (Chem. 1)(1,2-bis(4-aminophenyl)ethane when R1 and R2 are hydrogen and n=2) andmaterial represented by (Chem. 3) (1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride when R3 and R4 are methyl) as well asand an alignment material acquired by esterifying dehydrated condensateof represented by (Chem. 2) (paraphenyldiamine) and material representedby (Chem. 3) (1,3-dimethyl cyclobutane tetracarboxylic acid dianhydridewhen R3 and R4 are methyl) at a weight ratio of 1:1.

The applied alignment film is baked at 230° C. to imidize the alignmentfilm. In this case, the alignment material acquired by esterifyingdehydrated condensate of material represented by (Chem. 2)(paraphenyldiamine) and material represented by (Chem. 3) (1,3-dimethylcyclobutane tetracarboxylic acid dianhydride when R3 and R4 are methyl)has a rigid structure (hereinafter, referred to as the alignment filmhaving the rigid structure), and the alignment material acquired byesterifying dehydrated condensate of material represented by (Chem. 1)(1,2-bis(4-aminophenyl)ethane when R1 and R2 are hydrogen and n=2) andmaterial represented by (Chem. 3) (1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride when R3 and R4 are methyl) has aflexible structure (hereinafter, referred to as the alignment filmhaving the flexible structure).

Thereafter, the temperature of the substrate is brought down toapproximately room temperature. Further, since the substrate is thin,the temperature of the substrate is brought down in a short time whenthe substrate is removed from a baking furnace. In this state, linearlypolarized ultraviolet rays are irradiated to the alignment film for theoptical alignment. Uniaxiality is given to the alignment film of thehigh molecules as main chains of the alignment film of the highmolecules are cut in the polarization direction by the linearlypolarized ultraviolet rays. In this case, a volatile low-molecularmaterial or oligomer is generated by cutting a polymer. A polarizationexposure apparatus in which a Deep-UV lamp (ultrahigh-voltage He—Xe)manufactured by Ushio and a polarizer are combined is used and theultraviolet-rays are irradiated to the alignment film at 3 J/cm².

After the ultraviolet rays are irradiated, the substrate is heated at230° C. to volatilize a volatile low-molecular material. In this case,nonvolatile oligomer on the alignment film having the rigid structure isimmovable on the alignment film. Meanwhile, the nonvolatile oligomer onthe alignment film having the flexible structure may rotate on thealignment film and improve alignment orderliness.

FIG. 4 is a mimetic diagram illustrating by comparing an alignment filmstructure in the related art with an alignment film structure in thepresent invention. The upper part is the structure in the related artand the lower part is the structure in the present invention. Thematerial in the related art is formed only by the alignment film havingthe rigid structure, and the rigid structure and the flexible structurecoexist in the material in the present invention. In FIG. 4, thealignment film materials are mixed by the weight ratio of 1:1 andapplied onto a quartz substrate.

The left drawings of FIG. 4 are mimetic diagrams of the alignment filmstructure in which the alignment film is applied and heated at 230° C.for 10 minutes. In the related art, polyimide is regularly formed in alattice shape and has the rigid structure. In this regard, in thepresent invention, the rigid structure in which polyimide is formed inthe lattice shape and the flexible structure in which flexible polyimidecrosses flexibly coexist.

Thereafter, a state of cooling the substrate up to approximately normaltemperature and exposing the cooled substrate by using polarizedultraviolet rays is illustrated in a middle column of FIG. 4. In themiddle drawings of FIG. 4, a main chain of polyimide is cut and thealignment orderliness of the alignment film is thus revealed in thedirection of the polarization electric field vector of the ultravioletrays by the polarized ultraviolet rays. The above structure is the sameas the structure in the related art and the structure in the presentinvention.

Thereafter, a state in which the substrate is baked at 230° C. forapproximately 10 minutes is illustrated in right drawings of FIG. 4.Since the related art is formed by only polyimide having the rigidstructure, oligomer is immovable. Meanwhile, in the present invention,the rigid structure and the flexible structure coexist and both oligomerin the rigid structure and oligomer in the flexible structure rotate tothereby improve the alignment orderliness.

The above description will be summarized as follows. That is, in thestructure in the related art shown in the upper part of FIG. 4, rigidpolyimide having a large molecular extinction coefficient differencebetween the long-axis direction of the molecules and the short-axisdirection of the molecules is used as the alignment film material toincrease the alignment orderliness as much as possible. This is based onan idea that the alignment orderliness is increased by using a fact thata difference in density of polyimide in the E// direction and the E⊥direction after irradiating the polarized ultraviolet rays increases asthe molecular extinction coefficient difference increases because aphotolysis speed of polyimide is in proportion to the molecularextinction coefficient of polyimide. Herein, E// is a component parallelto the electric field vector of polarization and E⊥ is a componentvertical to the electric field vector of polarization.

However, polyimide having a large molecular extinction coefficientdifference is generally a high molecule that has high molecularlinearity and is rigid. As a result, since a molecular direction of aphotolysis product is fixed in a direction of a photolysis productionstate in spite of heating after polarization exposure, the alignmentorderliness is not increased.

Meanwhile, in the present invention shown in the lower part of FIG. 4,the alignment film material mixed with the flexible polyimide of whichthe main chain is cut by the polarized ultraviolet rays is used.Therefore, as shown in FIG. 5, a difference in density of the alignmentmolecules in the E// direction and the E⊥ direction can be increased andthe alignment orderliness can be increased as compared with thealignment film independently using the respective alignment filmmaterials.

FIG. 5 illustrates a relationship between a mixture ratio and thealignment orderliness when the rigid polyimide and the flexiblepolyimide are mixed. As known from FIG. 5, the alignment orderliness inthe case of using the alignment film material in which both polyimidesare mixed is higher than the case of using the alignment film in whichthe individual alignment film materials are independently used.

In FIG. 5, a sample illustrated in FIG. 4 is measured as below. Aspectrum of the polarized ultraviolet rays of a heated alignment film ismeasured, and a UV-absorbed two-color ratio (two-color ratio) which isan index of the alignment orderliness, that is, (A⊥−A//)/(A⊥+A//) isacquired from absorptiveness. Herein, A// is absorptiveness of analignment film in the E// direction and A⊥ is absorptiveness of thealignment film in the E⊥ direction. Further, when A is set as theabsorptiveness, there is a relationship of A=εCt. ε represents themolecular extinct coefficient, C represents a density of a predetermineddirectional molecule of polyimide, and t represents the thickness ofpolyimide.

In FIG. 5, a vertical axis represents an order parameter (OP) in anultraviolet ray having a wavelength of 245 nm and a horizontal axisrepresents wt % of the alignment film having the flexible structure onthe alignment film. Further, the order parameter (OP) has the samemeaning as the UV-absorbed two-color ratio. As seen from FIG. 5, a valueof the OP when the ratio of the flexible structure is 50 wt % is 0.51.When an anchoring strength of liquid crystals by the alignment film atthat time is measured, the anchoring strength is found to be 4.1 mJ/m².

As a comparative example, a measurement result of the OP by forming thealignment film in which only the alignment material having the rigidstructure acquired by esterifying dehydrated condensate ofparaphenyldiamine represented by (Chem. 2) and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride represented by (Chem. 3) when R3 and R4are methyl is used as the alignment film material is 0.48. Further, ameasurement result of the OP by forming the alignment film in which onlythe alignment material having the flexible structure acquired byesterifying dehydrated condensate of 1,2-bis(4-aminophenyl)ethanerepresented by (Chem. 1) when R1 and R2 are hydrogen and n=2 and1,3-dimethyl cyclobutane tetracarboxylic acid dianhydride represented by(Chem. 3) when R3 and R4 are methyl is used as the alignment filmmaterial is 0.44. That is, like the present invention, by mixing andusing the alignment film materials having the flexible structure and therigid structure, the OP, i.e., the UV-absorbed two-color ratio can beimproved.

In FIG. 5, the alignment film material having the flexible structure isused in 20 to 60 wt %, such that the OP, that is, the UV-absorbedtwo-color ratio may be set to 0.5 or more. Further, the alignment filmmaterial having the flexible structure is used in 80% or less, such thatthe UV-absorbed two-color ratio may be more than 0.48 which is the OPwhen the flexible structure is zero. In this case, the material havingthe flexible structure is more than 0 wt % and equal to or less than 80wt %.

As described above, according to the present invention, the orderparameter (OP), that is, the UV-absorbed two-color ratio can be improvedand the AC afterimage can be suppressed by improving the anchoringstrength of the liquid crystals by the alignment film.

In the example as above, as the alignment film material having theflexible structure, the alignment material acquired by esterifyingdehydrated condensate of material represented by (Chem. 1)(1,2-bis(4-aminophenyl)ethane when R1 and R2 are hydrogen and n=2) andmaterial represented by (Chem. 3) (1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride when R3 and R4 are methyl) is used. Inaddition, the alignment film material having the flexible structure maybe configured by using the alignment material acquired by esterifyingdehydrated condensate of material represented by (Chem. 4)(4,4′-Diaminodiphenyl ether) and a derivative thereof and materialrepresented by (Chem. 3) (,3-dimethyl cyclobutane tetracarboxylic aciddianhydride when R3 and R4 are methyl).

Further, in the example as above, as the alignment film material havingthe rigid structure, the alignment material acquired by esterifyingdehydrated condensate of material represented by (Chem. 2)(paraphenyldiamine) and material represented by (Chem. 3) (1,3-dimethylcyclobutane tetracarboxylic acid dianhydride when R3 and R4 are methyl)is used. In addition, the alignment film material having the rigidstructure may be configured by using the alignment material acquired byesterifying dehydrated condensate of a paraphenylene diamine derivativerepresented by (Chem. 5) and material represented by (Chem. 3)(1,3-dimethyl cyclobutane tetracarboxylic acid dianhydride when R3 andR4 are methyl). Further, condensate of 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride and diamine as well as an esterifiedproduct may also be appropriately used as the alignment material of thepresent invention.

What is claimed is:
 1. A liquid crystal display device, comprising: aTFT substrate where an alignment film is formed on a pixel having apixel electrode and a TFT; an opposed substrate opposed to the TFTsubstrate and where an alignment film is formed on a color filter; andliquid crystals interposed between the alignment film of the TFTsubstrate and the alignment film of the opposed substrate, wherein eachof the alignment films is subjected to optical alignment processing, andeach of the alignment films uses: a first alignment film materialcomprising a dehydrated condensate of 1,2-bis(4-aminophenyl)ethane and1,3-dimethyl cyclobutane tetracarboxylic acid dianhydride or a firstalignment film material acquired by esterifying the dehydratedcondensate of 1,2-bis(4-aminophenyl)ethane and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride, and a second alignment film materialcomprising a dehydrated condensate of paraphenyldiamine and 1,3-dimethylcyclobutane tetracarboxylic acid dianhydride or a second alignment filmmaterial acquired by esterifying the dehydrated condensate ofparaphenyldiamine and 1,3-dimethyl cyclobutane tetracarboxylic aciddianhydride.
 2. The liquid crystal display device according to claim 1,wherein the first alignment film material is more than 0 wt % and equalto or less than 80 wt % with respect to a total weight of the firstalignment film material and the second alignment film material.
 3. Theliquid crystal display device according to claim 1, wherein the firstalignment film material is 20 wt % or more or 60 wt % or less withrespect to the total weight of the first alignment film material and thesecond alignment film material.
 4. An alignment film material, whereinthe alignment film material is a mixture of a first alignment filmmaterial comprising a dehydrated condensate of1,2-bis(4-aminophenyl)ethane and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride or a first alignment film materialacquired by esterifying the dehydrated condensate of1,2-bis(4-aminophenyl)ethane and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride, and a second alignment film materialcomprising dehydrated condensate of paraphenyldiamine and 1,3-dimethylcyclobutane tetracarboxylic acid dianhydride or a second alignment filmmaterial acquired by esterifying the dehydrated condensate ofparaphenyldiamine and 1,3-dimethyl cyclobutane tetracarboxylic aciddianhydride.
 5. The alignment film material according to claim 4,wherein the first alignment film material is more than 0 wt % and equalto or less than 80 wt % with respect to a total weight of the firstalignment film material and the second alignment film material.
 6. Thealignment film material according to claim 4, wherein the firstalignment film material is 20 wt % or more or 60 wt % or less withrespect to the total weight of the first alignment film material and thesecond alignment film material.
 7. The alignment film material accordingto claim 4, wherein the alignment film material is an optical alignmentfilm material.
 8. The alignment film material according to claim 5,wherein the alignment film material is an optical alignment filmmaterial.
 9. The alignment film material according to claim 6, whereinthe alignment film material is an optical alignment film material.
 10. Aliquid crystal display device, comprising: a TFT substrate where analignment film is formed on a pixel having a pixel electrode and a TFT;an opposed substrate opposed to the TFT substrate and where an alignmentfilm is formed on a color filter; and liquid crystals interposed betweenthe alignment film of the TFT substrate and the alignment film of theopposed substrate, wherein the alignment films are subjected to opticalalignment processing, and each of the alignment films comprises: a firstalignment film material comprising a dehydrated condensate of1,2-bis(4-aminophenyl)ethane and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride or a first alignment film materialacquired by esterifying the dehydrated condensate of1,2-bis(4-aminophenyl)ethane and 1,3-dimethyl cyclobutanetetracarboxylic acid dianhydride, and a second alignment film materialcomprising a dehydrated condensate of paraphenyldiamine and 1,3-dimethylcyclobutane tetracarboxylic acid dianhydride or a second alignment filmmaterial acquired by esterifying the dehydrated condensate ofparaphenyldiamine and 1,3-dimethyl cyclobutane tetracarboxylic aciddianhydride.
 11. The liquid crystal display device according to claim10, wherein the first alignment film material is more than 0 wt % andequal to or less than 80 wt % with respect to a total weight of thefirst alignment film material and the second alignment film material.12. The liquid crystal display device according to claim 10, wherein thefirst alignment film material is 20 wt % or more or 60 wt % or less withrespect to the total weight of the first alignment film material and thesecond alignment film material.